Sharktooth Hill Geology
Student Handout: Rock Unit Descriptions
Alluvium [Qa] – Unconsolidated sand, gravel and cobbles; clasts of igneous and metamorphic composition. Age: Holocene (0-1 m.y.)
Kern River Fm [QTkr] – sand-dominated unit, fluvial deposited; gravel beds with igneous and metamorphic clasts common, as are clay-rich silt beds; sands are light-colored (tan); poorly fossiliferous. Age: Upper Miocene-Pleistocene (1-6 m.y.)
Bena Gravel Fm [Tbg] – Extremely coarse pebbles and cobbles mixed with sand; poorly sorted; deposited in a non-marine environment very close to the Sierra Nevada; pebbles and cobbles are igneous and metamorphic; contains few, if any, fossils except for petrified wood. Age: Miocene(6-16 m.y.)
Chanac Fm [Tch] – Boulder and cobble gravel with sand; unconsolidated; boulders made of metamorphic and igneous rock; cobbles may be light or dark colored. Age: Miocene (8-10 m.y.)
Round Mountain Silt [Trm] – Shale-y clay-rich siltstone, gray to light brown; lower half is dominated by gray diatomaceous clay shalewith rare sandy beds; one bed of vertebrate fossils (the Bone Bed) exists in the upper half, a few beds contain invertebrates (gastropods) throughout the formation. Age: Miocene (14-16 m.y.)
Olcese Fm [To] – Dominated by medium to coarse grained sandstone; some beds of finer sand and conglomerate exist. The upper half is very fossiliferous with invertebrates such as pelecypods and gastropods. The lower half is somewhat finer grained with fine grained sandstone and siltstone. Units were deposited in shallow marine/intertidal zones. Age: Miocene (16-18 m.y.)
Freeman-Jewett Fm [Tfj] – The upper part is the Freeman Silt, a light to brownish gray, friable, micaceous clayey siltstone. Some bentonitic (volcanic ash) beds exist; fossils include small pelecypods and fish scales. The Jewett sand occupies the lower part of this unit. It is gray to brownish gray, fossiliferous silt-y sand with local bentonitic and calcareous beds; “cannonball” reddish brown concretions are common. These concretions are fossiliferous and often have worm borings. Age: Miocene (18-24 m.y.)
Pyramid Hill Sandstone (Member of the Freeman-Jewett Fm) [Tp, Tjp] – Sandstone, gray to brownish gray;locally contains bentonitic and calcareous beds. The lowestbeds contain very poorly sorted/angular quartz grains with black pebbles and is known as the “grit” zone. Age: Miocene (23-24 m.y.)
Vedder Sand [Tv] – The upper part of formation contains multiple thick beds of pebbly sandstone poorly-sorted, light tan and light gray; common oyster fossils and scattered black pebbles; shallow marine. The lower part of the formation is dominated by grayish-white micaceous sandstone, but is finer-grained and silt-y. Age: Oligocene (25-36 m.y.)
Walker Fm [Tw, Tw-f, Tf] – Non-marine siltstone and clay shale with sand lenses; intertongues/grades westward into shale of the Famoso Shale Member; Walker Fm. shale weather light gray to light green; sandstones are greenish-white and poorly sorted. Age: Eocene (37-45 m.y.)
Geologic Map Key
Thin black line – Contact between two rock units
Thick black line/Dashed line – Fault
Geologic Time Scale
This is a standard geologic time scale listing names of major time periods with time span information. Geologists have subdivided periods in Earth's history is measured periods spanning millions of years (Ma). Segments of time periods have been named to help define the chronology of events (such as mountain range formation), the formation of rock units (such as the age of a lava flow), the age of fossils, organizing geologic map units, and other purposes.
(USGS:
SJVRocks!!
CSUBakersfield
1
Department of Geological Science